1. Field of the Invention
This invention relates to a system and method for measuring, storing and communicating sensor readings from a patient to a central system for display and analysis.
2. Discussion of the Related Art
For certain medical conditions, such as head trauma, it is necessary to place sensors on and in a patient to take continuous sensor readings. One shortcoming of the prior art is the need to wire the sensors to receiving and recording units located near the patient. The wires, especially leading to implanted sensors, cause difficulty for caregivers to move and treat the patient, both in and out of bed. In response, wireless sensor systems were developed that record the sensor data and do not tether the patient to wired receivers. The sensor data is transmitted wirelessly to the receiver. However, continuous wireless data transmission draws a significant amount of power. Since the sensors are wireless, they must rely on battery power and the continuous wireless transmission shortens the battery life and thus the operational life of the sensor.
To overcome some of the above shortcomings, U.S. Pat. No. 4,519,401 to Ko et al. (“Ko”) discloses a minimized “pulse” power scheme wherein the sensors and transmitters are placed in a low power cycle when readings are not being taken and then pulse powered up to take a sensor reading and transmit it to a receiver. This power conservation scheme is useful for sensor readings that are only taken at intervals and not continuously. Continuous data sampling would defeat Ko's pulse power scheme, as the sensors and transmitter can never power down.
U.S. Pat. No. 6,533,733 to Ericson et al. (“Ericson”) discloses a sensing system wherein the sensor readings are continuously read and stored. The stored data is then periodically transmitted to a receiver. The sensors are continuously powered and transmitter is also continuously powered and draws additional power during power transmission. Ericson realizes that this system is power consumptive and solves the problem by using a combination of power supplies. Ericson is silent regarding powering down the system and Ericson's system could not take continuous readings without constant power. Further, since Ericson's sensor data is stored, the sensor readings are not resented to the caregiver in approximately real-time. Thus, there is a time lag between when the sensor data is taken and displayed. Ericson compensates for this lag by providing the sensor controller with an alarm function to notify a caregiver of an anomalous sensor reading.
U.S. Pat. No. 6,731,976 to Penn et al. (“Penn”) discloses a passive sensing system wherein sensor readings are taken and transmitted only when powered externally. The sensing and transmission only last as long as the external power is supplied. This embodiment provides “real-time” sensor data but only while the system is externally powered. Further, Penn discloses an embodiment of providing a power supply for the system but, as Ericson does, Penn takes and stores the sensor data but does not disclose powering down the transmitter to conserve energy. Further, Penn does not disclose how to compensate for the lag between when the sensor data is taken and when it is transmitted.
Thus, there is a need in the art for a sensor system that can take continuous readings and provide the sensor data to a caregiver is pseudo-real-time. Further, there is a need to conserve power of the sensing device and transmitter by powering down the transmitter and transmitting the sensor data only over bursts.